[IbizaFR]

Hello!

I am writing code to solve 2D Steady Laminar Backwards Facing Step problem for Reynolds number up to 400 through finite differences with dimensionless 2D Navier-Stokes equations. The boundary conditions are the following:

Inlet: Parabolic profile for u, v=0, pressure calculated by the pseudo-compressibility continuity equation.

Walls: u=v=0, pressure calculated by the pseudo-compressibility continuity equation.

Outlet: θu/θx=0, θv/θx=0, p=0.

I am running the code but after the step the flow has an upwards direction where it would be expected going downwards with recirculation area.

Any help?

Thank you very much.

[FMDenaro]

Originally Posted by IbizaFR

Hello!

I am writing Matlab code to solve 2D Steady Laminar Backwards Facing Step problem for Reynolds number up to 400 through finite differences with dimensionless 2D Navier-Stokes equations. The boundary conditions are the following:

Inlet: Parabolic profile for u, v=0, pressure calculated by the pseudo-compressibility continuity equation.

Walls: u=v=0, pressure calculated by the pseudo-compressibility continuity equation.

Outlet: θu/θx=0, θv/θx=0, p=0.

I am running the code but after the step the flow has an upwards direction where it would be expected going downwards with recirculation area.

Any help?

Thank you very much.

I suggest to debug the code to find some bugs... have a look to the pressure equation that must have suitable Neumann BC.s

[IbizaFR]

Thank you FMDenaro.

Are the boundary conditions that I am using correct except for the pressure boundary conditions?

[FMDenaro]

Originally Posted by IbizaFR

Thank you FMDenaro.

Are the boundary conditions that I am using correct except for the pressure boundary conditions?

I suggest not to use the constant pressure at the exit but the condition derived from the fact that you supposed du/dx=0 in the continuity equation evaluated at the exit. You will also easily see that you get v=0 along the outflow.

[IbizaFR]

Thank you. I will check it.

[FMDenaro]

Are you using a second order central discretization on staggered grid?

[IbizaFR]

I am working with finite differences and in some cases with second order central discretization and in another cases with forward or backward discretization.

[FMDenaro]

what about the colocation of the variables on the grid?

[IbizaFR]

Originally Posted by FMDenaro

what about the colocation of the variables on the grid?

I am using finite differences with the same arrangement for all variables u,v,p.

[selig5576]

In your pressure solver are you sure your treating the outlet boundary correctly? For a collocated grid and using the classical Rhie-Chow method your PPE will have at the outlet.

[IbizaFR]

Originally Posted by IbizaFR

Hello!

I am writing code to solve 2D Steady Laminar Backwards Facing Step problem for Reynolds number up to 400 through finite differences with dimensionless 2D Navier-Stokes equations. The boundary conditions are the following:

Inlet: Parabolic profile for u, v=0, pressure calculated by the pseudo-compressibility continuity equation.

Walls: u=v=0, pressure calculated by the pseudo-compressibility continuity equation.

Outlet: θu/θx=0, θv/θx=0, p=0.

I am running the code but after the step the flow has an upwards direction where it would be expected going downwards with recirculation area.

Any help?

Thank you very much.

Hello!

I wrote SIMPLE algorithm for the same problem but the velocity field is not the expected.
Is there any advice about the correct boundary conditions of the problem?

Thank you.